Merge Sorted Lists

MergeSortedList.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    
        if(l1 == null || l2 == null) {
            return l1 != null ? l1 : l2;
        }
        ListNode head = null;
    
        if(l1.val < l2.val) {
            head = l1;
            l1 = l1.next;
        } else {
            head = l2;
            l2 = l2.next;
        }
        
        ListNode traverse = head;
        while(l1 != null && l2 != null) {
            if(l1.val < l2.val) {
                traverse.next = l1;
                l1 = l1.next;
            } else {
                traverse.next = l2;
                l2 = l2.next;
            }
            
            traverse = traverse.next;
        }
        
        traverse.next = l1 != null ? l1 : l2;
        
        return head;
    }
}